The effect of temperature on the performance of audiometric mechanical coupler systems

Measurements of mechanical coupler performance have been made over the temperature range 13 degrees C to 33 degrees C to investigate the change of force sensitivity level and mechanical impedance level with temperature for frequencies in the range 125 Hz to 5000 Hz. In addition, the temperature dependence of the voltage output of the mechanical coupler system has been measured for a coupler driven by a Radioear type B-71 bone vibrator, to investigate the net effect of these changes on an audiometer calibration. Very clear dependence on temperature has been found for all three parameters at some frequencies. In particular, coefficients approaching 0.6 dB/degrees C have been found for the rate of change of force sensitivity level at higher frequencies, and when driven by a bone vibrator coefficients around 0.5 dB/degrees C have been measured for the voltage output, again at the higher frequencies. This strong dependence of the performance of the mechanical coupler on temperature has implications for all those working in audiometric calibration, and especially for those involved in providing calibrations of audiometers in situ, where the mechanical coupler is transported from site to site and may well be exposed to extremes of temperature during transportation.